Modern motor vehicle design emphasizes safety features which protect vehicle occupants in the event of a collision. To this end, reinforced structures have been developed with the objective of increasing motor vehicle body strength without unduly increasing overall vehicle weight and cost.
As will be appreciated by those skilled in the art, perhaps the most significant advance in recent years in materials technology for motor vehicle design is the development of composite materials. In that regard, the inventor of the present invention has developed a number of composite structures and methods of forming composites and their constituent elements. For example, in U.S. Pat. No. 4,737,407 which issued Apr. 12, 1988, the inventor of the present application discloses thermoset plastic pellets and a method and apparatus for making the pellets. In U.S. Pat. No. 4,751,249 which issued June 14, 1988, the inventor of the present invention discloses a reinforcement insert for a structural member and a method of making and using the insert. In U.S. Pat. No. 4,836,516 (the disclosure of which is incorporated herein by reference), the inventor of the present invention discloses a filled tubular torsion bar which is reinforced by a mixture of a resin-based filler. In U. S. Pat. No. 4,923,902, issued May 8, 1990 (the disclosure of which is incorporated herein by reference), the present inventor discloses a method of making a composite door beam which is mounted within the door cavity of a vehicle. The door beam includes a lightweight channel-shaped member having a foam core disposed therein.
Most motor vehicle doors generally have an outer door panel or skin and an inner door panel in spaced relation such that a door cavity is defined. Disposed within the door cavity are various door systems such as locking mechanisms and lowerable window actuating means. Without further structural reinforcements, these hollow motor vehicle doors are often not adequately resistant to side impacts. That is, when a motor vehicle door of this type is struck during a collision or the like, the inner and outer door panels offer only limited resistance to side intrusion. Hence, it will be appreciated that there is a need for structurally reinforced motor vehicle doors to provide greater impact resistance.
Reinforcing structures, known variously as impact beams, intrusion beams, guard beams and the like, have also been proposed by others for use in motor vehicle doors to provide improved side impact resistance. For example, U.S. Pat. No. 4,090,734 to Inami et al., entitled "Reinforcement Member for an Automobile Door," discloses a door beam that provides side impact-resistant strength to a vehicle door. The door beam includes a central section formed from a plate having end pieces attached thereto. The central section is disclosed as having an undulation. In U.S. Pat. No. 3,964,208 to Renner et al., entitled "Door for Vehicle, Especially Passenger Motor Vehicle," there is disclosed a reinforced motor vehicle door which includes an intermediate panel with undulations which form cavities when mated to the outer door skin. It is stated that these cavities can be filled with a synthetic resin-based foam material. In U.S. Pat. No. 4,378,395 to Asoshina et al., entitled "Reinforcing Material," a material for reinforcing a panel is disclosed which includes a resin that conforms to a preselected surface of a vehicle door. In U. S. Pat. No. 3,868,796 to Bush, entitled "Side Door Intrusion Protection," a composite beam for reinforcing an automobile door is disclosed in which the outer skin panel of the vehicle door is integrated as part of the beam. A corrugated inner panel is welded to the outer skin, and the voids created thereby are filled with foam.
In U.S. Pat. No. 4,013,317 to Reidelbach et al., entitled "Lateral Protection for Motor Vehicles," a door beam and door reinforcement structure are disclosed which comprise a sheet-metal closure panel. In U. S. Pat. No. 4,3807,911 to Pavlik, entitled "Reinforcement Means for Resisting Side Impacts Against an Automobile Door," a horizontal door beam reinforcement is disclosed which includes a beam that is secured by an adhesive or the like to the outer door panel. The beam may include channel sections for increased strength. In European Patent Application No. 87-251774/36, a reinforcement structure is disclosed for a car door which comprises a plastic layer in which a metal reinforcing strip is embedded. In European Patent No. 59-34921, a hat-shaped section in the nature of an impact beam is described which is mounted within a vehicle door to increase side impact strength.
As will be appreciated by those skilled in the art, Federal Motor Vehicle Safety Standards mandate that vehicle side doors have a minimum specified strength in resisting side impacts. Side intrusion resistance is typically measured with a hydraulic ram which is pressed into the outer door panel. As the door is crushed 18 inches into the vehicle, specific loads must be met.
In order to more fully appreciate the performance characteristics of the present invention, an explanation of flexure theory of a simple beam will now be described. In a simple beam, the beam are being supported such that the span between the supports is free to move in the vertical plane under a load perpendicular to the transverse beam axis. In three-point beam deflection testing, and referring now to FIG. 9 of the drawings, a load P perpendicular to the transverse axis of beam A having span L is applied at the mid-point of the beam. In other words, FIG. 9 illustrates a simple beam having a concentrated load applied an equal distance from the end supports. Accordingly, the maximum bending moment (lb.-in.) is equal to the Product of P, concentrated load (lb.) times the length of the beam (in.) divided by 4: ##EQU1## Graphically, in terms of a moment diagram this relationship is shown in FIG. 10 of the drawings. The theoretical maximum elastic deflection at the center of the span may be determined as follows: ##EQU2## Where Y is maximum deflection in inches, P is concentrated load in pounds, E is modulus of elasticity in PSI, and I is moment of inertia in inches raised to the fourth power. As will be explained more fully herein, the novel impact beam provided by the present invention optimizes the beam's strength for centrally disposed loads in a highly effective manner which reduces both cost and beam weight.
It will be appreciated that the peak bending load of an impact beam is a function of the tensile strength of the beam. Hence, for the purposes of impact beam performance, it is desirable to optimize the ratio of the maximum bending moment to the tensile strength of the beam. In addition, it is also known that the desired performance characteristics of a particular beam structure are difficult to obtain in those designs which exhibit buckling during deformation. Buckling often occurs in door beams which are formed as hollow round tubes or single hat-shaped structures.
Although large, heavy, structural reinforcements provide increased side-intrusion resistance, they also add to the total vehicle weight and usually increase material production costs. Moreover, in new automotive designs there is less space available within the vehicle for the placement of reinforcement door beams. Therefore, it would be desirable to provide a lightweight, compact door beam having a design which easily fits within a vehicle door cavity. By providing a strong yet lightweight door beam, total mass savings could be achieved. In addition, it would be desirable to provide such a door beam which could easily be fabricated from a minimum number of parts. The present invention provides such an impact or intrusion door beam having the aforementioned desirable characteristics and features.
Therefore, it is an object of the present invention to provide an improved lightweight composite impact beam for use in reinforcing a motor vehicle door.
Still another object of the present invention is to provide an improved impact-resistant motor vehicle door.
It is also an object of this invention to provide a method of manufacturing a composite impact beam having a syntactic foam core localized at the beam mid-span.